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Integrative and Comparative Biology 2004 44(2):130-139; doi:10.1093/icb/44.2.130
© 2004 by The Society for Integrative and Comparative Biology
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Agricultural Food Subsidies, Migratory Connectivity and Large-Scale Disturbance in Arctic Coastal Systems: A Case Study1

R. L. Jefferies2,1, R. F. Rockwell2 and K. F. Abraham3
1 Department of Botany, University of Toronto, 25, Willcocks St., Toronto, Ontario M5S 3B2, Canada
2 Department of Ornithology, American Museum of Natural History, Central Park West, New York, New York 10024
3 {ddagger}Ontario Ministry of Natural Resources, 300 Water St., Peterborough, Ontario K9J 8M5, Canada

An allochthonous input can modify trophic relationships, by providing an external resource that is normally limiting within a system. The subsidy may not only elicit a growth response of the primary producers via a bottom-up effect, but it also may lead to runaway herbivore growth in the absence of increased predation. If the consumer is migratory and predation is similarly dampened in the alternative system, the increased numbers may produce a top-down cascade of direct and indirect effects on an ecosystem that may be a great distance from the source of the subsidy. In an extreme case, it can lead to a catastrophic shift in ecosystem functioning as a result of biotic exploitation that produces an alternative stable state. The loss of resilience is particularly sensitive to herbivore density which can result in two different outcomes to the vegetation on which the consumer feeds. Over-compensatory growth of above-ground biomass gives way to sward destruction and near irreversible changes in soil properties as density of a herbivore increases. A striking temporal asymmetry exists between a reduction in the consumer population and recovery of damaged vegetation and degraded soils.


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